Bash script: Stay Out Of Trouble

String Comparison Result 

string1 = string2                                            True if the strings are equal. 

string1 != string2                                          True if the strings are not equal. 

-n string                                                            True if the string is not null. 

-z string                                                            True if the string is null (an empty string).

Arithmetic Comparison Result 

expression1 -eq expression2 True if the expressions are equal. 

expression1 -ne expression2 True if the expressions are not equal. 

expression1 -gt expression2 True if expression1is greater than expression2. 

expression1 -ge expression2 True if expression1is greater than or equal to 

expression2. 

expression1 -lt expression2 True if expression1is less than expression2. 

expression1 -le expression2 True if expression1is less than or equal to 

expression2. 

! expression True if the expression is false, and vice versa.

File Conditional Result 

-d file True if the file is a directory. 

-e file True if the file exists. Note that, historically, the -e option has not 

been portable, so -f is usually used. 

-f file True if the file is a regular file. 

-g file True if set-group-id is set on file. 

-r file True if the file is readable. 

-s file True if the file has nonzero size. 

-u file True if set-user-id is set on file. 

-w file True if the file is writable. 

-x file True if the file is executable. 

Debugging Scripts 

Command Line Option setOption Description 

sh -n